Low pressure mercury vapor discharge lamp with amalgam

ABSTRACT

Mercury vapor discharge lamps of the fluorescent type having an improved amalgam. The amalgam is formed, in addition to mercury, of two amalgam-forming metals of which one is an alkali metal or an alkaline earth metal (preferably magnesium). The invention also includes lamp components containing the improved amalgam on a surface thereof. The preferred amalgam-forming metals are indium in an amount of from 95 to 50 mole percent and magnesium in an amount of from 5 to 50 mole percent of the total amalgamforming constituents. Mercury is preferably in an amount between 5 and 40 mole percent of the total amalgam (mercury plus the amalgam-forming constituents).

United States Patent 1191 Franck et a1.

LOW PRESSURE lVIERCURY VAPOR DISCHARGE LAMP WITH AMALGAM Inventors: Gunter Franck, Ebenhausen; Lothar Busch, Munich, both of Germany 21 Appl. No.1 490,986

[30] Foreign Application Priority Data Aug 1, 1973 Germany 2339056 US. Cl 313/490; 313/178 Int. Cl. HOlJ 61/28 Field of Search 313/490, 174, 178; 252/1814, 181.7; 75/169 References Cited UNITED STATES PATENTS 3,263,] 11 Doering 313/490 [451 Sept. 16, 1975 3,629,641 12/1971 Hofmann et al. 313/490 X Primary ExaminerPalmer C. Demeo Attorney, Agent, or FirmFlynn & Frishauf ABSTRACT Mercury vapor discharge lamps of the fluorescent type having an improved amalgam. The amalgam is formed, in addition to mercury, of two amalgamforming metals of which one is an alkali metal or an alkaline earth metal (preferably magnesium). The invention also includes lamp components containing the improved amalgam on a surface thereof. The preferred amalgam-forming metals are indium in an amount of from 95 to 50 mole percent and magnesium in an amount of from 5 to 50 mole percent of the total amalgam-forming constituents. Mercury is preferably in an amount between 5 and 40 mole percent of the total amalgam (mercury plus the amalgam-forming constituents).

23 Claims, 3 Drawing Figures PATENTEUSEP isms I Q 7 906 sum 1 9 3 FIG.1

LOW PRESSURE NIERCURY VAPOR DISCHARGE LAMP WITH AMALGAM BACKGROUND OF THE INVENTION This invention relates to low pressure mercury vapor discharge lamps of the fluorescent type. These lamps generally have high electrical and/or thermal loading. In these lamps, the equilibrium vapor pressure is determined by an amalgam which contains at least two amalgam-forming metals.

The functioning of such lamps is affected by the composition of the amalgam and also the positioning of the amalgam within the lamp. The function of the lamp is affected by changes in the composition which include both changes in the amalgam-forming metal or metals and in the relative proportions of each. It is necessary to take the foregoing into consideration to design lamps having particular utility in special fields of application and also in order to produce a multi-purpose lamp to the extent that this is possible.

It is known that the amalgam may comprise a plurality of amalgam-forming metals, see US. Pat. specification No. 3,007,071, US. Pat. specification No. 3,160,778, DT Pat. specification No. 1,149,818. Amalgams containing several amalgam-forming metals are used when it is desired that the amalgam-forming metal attains desired predetermined physical characteristics so that optimum processing conditions may be employed to manufacture the lamp with the amalgamforming metal in the desired location within the lamp, see US. Pat. application Ser. No. 476,478, filed June 4, 1974, which is hereby incorporated by reference.

It is desired to obtain improved lamps having desirable luminous flux characteristics over a considerable temperature range and which are manufactured economically, particularly with regard to the amalgamforming constituents.

SUBJECT MATTER OF THE INVENTION The present invention provides improved lowpressure mercury vapor discharge lamps of the fluores cent type comprising an elongated light transmitting envelope having electrodes sealed into its ends. The electrodes are located within the lamp by electrode positioning means. The lamps contain at least one amalgam which determines the equilibrium vapor pressure during the operation of the lamp on an interior surface thereof. Generally, the amalgam is located on the electrode positioning means or on a foil connected to the electrode positioning means. The improved lamps of the present invention contain amalgams formed from, in addition to the mercury, at least two amalgamforming metals also referred to as amalgam-forming constituents. One of the amalgam-forming metals is selected from the group consisting of alkali metals and alkaline earth metals, and is preferably magnesium.

The present invention also provides lamp components, i.e., electrode supports and the electrode housing which provides or supports a surface containing the aforesaid amalgam-forming constituents which when incorporated into a completed lamp provide the lamps of the present invention containing the aforedescribed amalgam.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a fluorescent lamp with an amalgam positioned on a portion of the flare stem;

FIG.- 2 illustrates a perspective view of a modification of the FIG. 1 embodiment illustrating the amalgam located on a separately supported foil; and

FIG. 3 is a graph illustrating the relative luminous flux /d plotted against ambient temperature of the lamp in C.

The reference to metal and to constituent in connection with the terms amalgam-forming metal and amalgam-forming constituent refers to both elemental metals and alloys. As noted, the amalgams of the present invention are formed from, in addition to mercury, at least two amalgam-forming metals or constituents. One of these is an alkali or alkaline earth metal. The other amalgam-forming metal (or constituent) is one which fonns an alloy together with the alkali metal or alkaline earth metal constituent which has a lower melting point than the said alkali metal or alkaline earth metal constituent of the consequent amalgam-forming alloy. The lower the melting point of said consequent amalgamforming alloy, the higher is the diffusion velocity as a general rule.

The amalgam-forming metal (constituent) which is present in addition to the alkaline metal or alkaline earth metal constituent should have the desirable characteristic of good adhesion to the supporting surface on which it is located. It should also have a low vapor pressure and readily take up and give off mercury and form, together with the said alkali metal or said alkaline earth metal constituent, a solid or solid/liquid mixed phase. Preferred amalgam-forming metals which meet these criteria are indium and/or lead and/or cadmium and/or tin. These metals may be further alloyed as disclosed in said US. patent application Ser. No. 476,478.

The preferred alkali metal or alkaline earth metal constituent is magnesium and the preferred other amalgam-forming constituent is indium. When utilizing the said magnesium and indium, the magnesium is in an amount from about 5 to 50 mole percent and, preferably, from 10 to 30 mole percent based on the total amalgam-forming metals. The amalgam formed from the indium and magnesium preferably contains from about 5 to 40 mole percent of mercury. The conventional thermally highly loaded lamps are improved when in accordance with the present invention they utilize an amalgam whose composition is about 1 mole of mercury, 6 moles of indium, and 1 mole of magnesium. Known high power lamps, i.e., those having a high electrical load, are improved in accordance with the present invention when the amalgam composition is about 1 mole of mercury, 10 moles of indium, and 1 mole of magnesium.

In general for a given amalgam, a portion of the amal gam-forming metal or when several amalgam-forming metals are included in the amalgam, one of the said amalgam-forming metals, may be substituted by another amalgarn-forming metal. It is, however, required that the concentration and temperature-dependence characteristics of the coefficient of activity'of mercury in the respective metals, i.e., the original amalgamforrning metal and the substituting amalgam-forming metal, are about the same. The lower the coefficient of activity of mercury in the substituting amalgamforming metal, the lower may be its molar share of the total amalgam-forming constituents in order to decrease the partial mercury pressure to the same extent. The major advantage of magnesium as a substituting amalgam-forming metal, in the sense that it substitutes for known amalgam-forming metals, is that a small amount of magnesium substantially reduces the coefficient of activity and, consequently, the mercury vapor pressure. When magnesium is used with indium, this results in a considerable savings of indium. The amount of indium may be reduced by about 40% as a general rule. Since the ratio of cost of magnesium to indium is about 1:20, this is of major economic importance.

The amalgamforming alloys composed of magnesium have the additional important advantage in that they are more solid (i.e., more coherent) than the corresponding indium. This is of particular advantage when using the spray-forming technique frequently employed to produce surfaces coated with indium as an amalgam-forming metal surface, for example, as disclosed in U.S. patent application Ser. No. 433,773, filed Jan. 16, 1974, which is hereby incorporated by this reference.

The amalgams of the lamps of the present invention containing mercury have the additional advantage that the time required for mercury absorption and dissipation is substantially reduced when using these amalgams, thus resulting in an improved run-up or start-up performance of the lamp. As a consequence, the lamps of the present invention usually employ only one runup or start-up amalgam.

The amalgam-forming metals and consequent amalgams are preferably positioned in the form of an annulus covering at least part of the flared portion of the stem, or disposed on a foil arranged in a semi-circle positioned near the electrode stem between the flare and press seal portions thereof.

The invention is further illustrated with reference to the drawings in which on FIG. 1, the light-transmitting lamp envelope 1 (usually transparent) has a phosphor coating 2 on its inner surface. It has an electrode stem 3 sealed into each of its ends. Electrode stem 3 comprises flare stem 4 and the stern press seal 5 through which the lead-in wires 6 and 7 extend, and also contains the exhaust tube 8. The lamp also contains an electrode coil 9 which is coated with an oxide paste. The electrode 9 is connected to the inner ends of leadin wires 6 and 7. Each stem flare 4 is provided with an amalgam-forming alloy 10 composed of 6 moles of indium and one mole of magnesium, preferably in the form of an annulus. The width of the annulus 10 is 3 mm. The amalgam-forming annulus 10 contains about 1.2 mg of magnesium and 34 mg of indium. mg of mercury is provided in the lamp. The ratio of mercury to the total amalgam-forming constituents (indium and magnesium) is 1 mole of mercury to 7 moles of alloy. The electrode coil 9 is surrounded by a cylindrical metal cap 11. Cap 11 is supported by wire 12. Cap 11 also functions as a supporting surface for an aJnalgamforming metal 13 of indium which forms an amalgam to facilitate start-up of the lamp.

In FIG. 2 identical parts are designated by the same reference numerals as in FIG. 1. In this embodiment of the invention an iron foil 14 in the form of a Vz cylindrical surface is positioned around the electrode stem 3 between the stem flare 4 and the stem press seal 5. The foil 14 is spot welded to wire 12 for support. The amalgam 15 is applied as a layer on foil 14 and determines the equilibrium vapor pressure during operation of the lamp. The composition of the amalgam 15 is I IO gI- The curve illustrated in FIG. 3 establishes that in the lamps of the present invention which include the aforespecified amalgams, the luminous flux varies very little with differences in ambient temperature. Thus, when the ambient temperature varies from 20 to C, the luminous flux decreases only 7%. When the ambient temperature is 70C, the luminous flux has a value which is 97% of the maximum value. This illustrates that lamps having the mixed amalgams of the present invention, when compared with prior art lamps containing an amalgam formed with indium as the amalgam-forming metal, have a broadened luminous flux/- temperature curve. As noted, FIG. 3 illustrates that when the ambient temperature is 70C, the lamps of the present invention have a decreased value of luminous flux relative to the maximum value of only 3%. This luminous flux value decreases to about 10% only when the ambient temperature has risen to about C. This establishes an improved and desired luminous fluxtemperature characteristic for the improved lamps of the present invention.

The first amalgam-forming constituent (the alkali metal or the alkaline earth metal) is in an amount between 5 and 50 mole percent of the total of amalgamforming constituents, suitably between 10 and 30 mole percent. A

In addition to the preferred magnesium, other useful amalgam-forming metals from the alkali metals and alkaline earth metals include sodium, potassium, calcium, and strontium.

We claim:

1. A low pressure mercury vapor discharge lamp of the fluorescent type comprising an elongated lighttransmitting envelope having electrodes sealed into its ends, and support for at least one amalgam which determines the equilibrium vapor pressure during operation of the lamp on an interior surface of said lamp, said amalgam comprising mercury, and an amalgamforming composition containing at least two amalgamforming metal constituents, the improvement wherein said amalgam-forming composition comprises a first amalgam-forming constituent selected from the group consisting of the alkali metals and the alkaline earth metals, and a second amalgam-forming metal constituent comprising indium.

2. The lamp of claim 1 wherein said second amalgamforming constituent is at least one metal which form an alloy with said first amalgam-forming constituent, said alloy having a melting point which is lower than the melting point of said first amalgam-forming constituent.

3. The lamp of claim 2 wherein said second amalgamforming constituent also contains at least one metal selected from the group consisting of lead, cadmium and tin.

4. The lamp of claim 1 wherein said first amalgamforming constituent is magnesium.

5. The lamp of claim 2 wherein said first amalgamforming constituent is magnesium.

6. The lamp of claim 3 wherein said first amalgamforming constituent is magnesium.

7. The lamp of claim 6 wherein magnesium comprises between about 5 and 50 mole percent of the total of amalgam-forming constituents and indium comprises between about 95 and 50 mole percent of the total amalgam-forming constituents, and mercury comprises between about 5 and 40 mole percent of the total amalgam.

8. The lamp of claim 6 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 6 moles of indium, and 1 mole of magnesium.

9. The lamp of claim 6 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, moles of indium, and 1 mole of magnesium.

10. The lamp of claim 4 wherein at least one of said electrodes is supported by an electrode stem comprising a stern flare and a stem press seal and wherein said amalgam is in the form of an annulus on said stem flare.

l 1. The lamp of claim 4 wherein said electrodes are supported by electrode positioning means and wherein said amalgam is coated on a base sheet, said base sheet being supported by said electrode positioning means.

12. The lamp of claim 7 wherein magnesium comprises between 10 and mole percent of the total of magnesium and indium.

13. An electrode-containing component for fluorescent lamps comprising an electrode connected to an electrode positioning means, and having an amalgam which determines the equilibrium vapor pressure during operation of the lamp coated on at least a portion of said electrode positioning means, said amalgam comprising mercury and an amalgam-forming composition containing at least two amalgam-forming constituents, the improvement wherein said amalgam-forming composition comprises a first amalgam-forming constituent selected from the group consisting of the alkali metals and the alkaline earth metals, and a second amalgam-forming constituent which comprises indium.

14. The component of claim 13 wherein said first amalgam-forming constituent is magnesium.

15. The component of claim 14 wherein said second amalgam-forming constituent is indium, and wherein magnesium comprises between about 5 and 50 mole percent of the total of amalgam-forming constituents, and indium comprises between about and 50 mole percent of the total amalgam-forming constituents, and mercury comprises between about 5 and 40 mole percent of the total amalgam.

16. The component of claim 15 wherein said magnesium comprises between about 10 and 30 mole percent of the total of magnesium and indium.

17. The component of claim 15 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 6 moles of indium and 1 mole of magnesium.

18. The component of claim 15 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 10 moles of indium and 1 mole of magnesium.

19. The component of claim 14 wherein said electrode positioning means comprises a stem flare and a stem press seal and wherein said amalgam-forming composition is in the form of an annulus on said stem flare.

20. The component of claim 15 wherein said electrode positioning means comprises a stern flare and a stem press seal and wherein said amalgam-forming composition is in the form of an annulus.

21. The component of claim 13 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means.

22. The component of claim 15 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means.

23. The component of claim 16 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means. 

1. A low pressure mercury vapor discharge lamp of the fluorescent type comprising an elongated light-transmitting envelope having electrodes sealed into its ends, and support for at least one amalgam which determines the equilibrium vapor pressure during operation of the lamp on an interior surface of said lamp, said amalgam comprising mercury, and an amalgam-forming composition containing at least two amalgam-forming metal constituents, the improvement wherein said amalgam-forming composition comprises a first amalgam-forming constituent selected from the group consisting of the alkali metals and the alkaline earth metals, and a second amalgam-forming metal constituent comprising indium.
 2. The lamp of claim 1 wherein said second amalgam-forming constituent is at least one metal which form an alloy with said first amalgam-forming constituent, said alloy having a melting point which is lower than the melting point of said first amalgam-forming constituent.
 3. The lamp of claim 2 wherein said second amalgam-forming constituent also contains at least one metal selected from the group consisting of lead, cadmium and tin.
 4. The lamp of claim 1 wherein said first amalgam-forming constituent is magnesium.
 5. The lamp of claim 2 wherein said first amalgam-forming constituent is magnesium.
 6. The lamp of claim 3 wherein said first amalgam-forming constituent is magnesium.
 7. The lamp of claim 6 wherein magnesium comprises between about 5 and 50 mole percent of the total of amalgam-forming constituents and indium comprises between about 95 and 50 mole percent of the total amalgam-forming constituents, and mercury comprises between about 5 and 40 mole percent of the total amalgam.
 8. The lamp of claim 6 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 6 moles of indium, and 1 mole of magnesium.
 9. The lamp of claim 6 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 10 moles of indium, and 1 mole of magnesium.
 10. The lamp of claim 4 wherein at least one of said electrodes is supported by an electrode stem comprising a stem flare and a stem press seal and wherein said amalgam is in the form of an annulus on said stem flare.
 11. The lamp of claim 4 wherein said electrodes are supported by electrode positioning means and wherein said amalgam is coated on a base sheet, said base sheet being supported by said electrode positioning means.
 12. The lamp of claim 7 wherein magnesium comprises between 10 and 30 mole percent of the total of magnesium and indium.
 13. AN ELECTRODE-CONTAINING COMPONENT FOR FLUORESCENT LAMPS COMPRISING AN ELECTRODE CONNECTED TO AN ELECTRODE POSITIONING MEANS, AND HAVING AN AMALGAM WHICH DETERMINES THE EQUILIBRIUM VAPOR PRESSURE DURING OPERATION OF THE LAMP COATED ON AT LEAST A PORTION OF SAID ELECTRODE POSITIONING MEANS, SAID AMALGAM COMPRISING MERCURY AND AN AMALGAMFORMING COMPOSITION CONTAINING AT LEAST TWO AMALGAM-FORMING
 14. The component of claim 13 wherein said first amalgam-forming constituent is magnesium.
 15. The component of claim 14 wherein said second amalgam-forming constituent is indium, and wherein magnesium comprises between about 5 and 50 mole percent of the total of amalgam-forming constituents, and indium comprises between about 95 and 50 mole percent of the total amalgam-forming constituents, and mercury comprises between about 5 and 40 mole percent of the total amalgam.
 16. The component of claim 15 wherein said magnesium comprises between about 10 and 30 mole percent of the total of magnesium and indium.
 17. The component of claim 15 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 6 moles of indium and 1 mole of magnesium.
 18. The component of claim 15 wherein said amalgam comprises mercury, indium and magnesium in a mole ratio of 1 mole of mercury, 10 moles of indium and 1 mole of magnesium.
 19. The component of claim 14 wherein said electrode positioning means comprises a stem flare and a stem press seal and wherein said amalgam-forming composition is in the form of an annulus on said stem flare.
 20. The component of claim 15 wherein said electrode positioning means comprises a stem flare and a stem press seal and wherein said amalgam-forming composition is in the form of an annulus.
 21. The component of claim 13 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means.
 22. The component of claim 15 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means.
 23. The component of claim 16 wherein said amalgam-forming composition is coated on a base sheet, said base sheet being supported by electrode positioning means. 